In order to shorten the control time, particularly in case of high viscosity of the pressure medium, it was proposed in P 44 25 578.0 (P 7697) to turn on a supplemental pressure medium source at the beginning of the braking process which quickly makes available the required pressure of the pressure medium. As described in detail in the aforesaid P 44 25 578.0, such a measure offers the great advantage that the response of the regulation at the brakes can be considerably accelerated, even in the case of high viscosity of the pressure medium and thus considerable pressure losses due to the sluggish flow of the pressure medium inside the pressure lines.
It has turned out to be a certain disadvantage, however, that turning on such a supplemental pressure medium source can cause noise that may distract the driver precisely at the moment in time in which he is in a critical driving situation in need of regulation.
The object of the invention is to connect the supplemental pressure medium source to the control loop only if this is actually necessary to accelerate the regulation process.
This object is achieved, according to the invention, by turning on the supplemental pressure medium source as a function of a sufficiently large deviation from the desired value of the regulation parameter for driving dynamics, and a second factor which constitutes a measurement of whether turning on the pressure medium source is necessary for increasing the regulation rate under the environmental conditions. The invention brings the additional advantage that the supplemental pressure medium source is not operated unnecessarily and thus is under less mechanical stress, which contributes to increasing its reliability and service life.
In practice, it has proven particularly reasonable to make the connection of the supplemental pressure medium source dependent on the viscosity of the pressure medium. One parameter affecting the viscosity is the temperature of the pressure medium itself, so that it is advisable as an advantageous refinement of the invention to make connection dependent on the pressure medium temperature.
In order to save on additional sensors for measuring temperatures, the existing engine intake air temperature sensor can be used for estimating the temperature of the pressure medium.
Another possibility of estimating the temperature of the pressure medium consists of measuring wheel and vehicle response times according to the latter principle, the regulation behavior is evaluated for estimating the temperature.
In a preferred embodiment, the supplemental pressure medium source is activated only if the temperature of the pressure medium falls below a pre-determined temperature.
A particularly advantageous refinement of the invention is presented if the connection of the supplemental pressure medium source is made dependent on an additional parameter which corresponds to the gradient of the deviation of the actual value from the desired value of the control parameter. In other words, if the actual value of the driving dynamics parameter, such as the yaw angle velocity, differs only slightly from the desired set value, then it is not necessary for the regulation to take effect abruptly due to turning on the supplemental pressure medium source. Instead, it is then sufficient for the regulation to be operated only with the aid of the supply pump as a pressure medium source. The advantage is that in this way the regulation not only operates rather quietly, but also corrects the driving behavior of the vehicle more gently. This further contributes to the driving comfort of the operator. It is particularly advisable here as a refinement of the invention to make turning on the supplemental source dependent on the gradient of the difference of (one of the) following parameters: the steering angle, the yaw angle or the yaw angle velocity of the vehicle. The invention can also be applied advantageously if, instead of that, the gradient of the difference of the transverse accelerations of the vehicle or of the velocities of the vehicle serves as the criterion for turning on the supplemental pressure medium source.
An additional improvement of the invention can consist in making the additional parameters on which the turning on of the supplemental source depends not dependent or not solely dependent on the gradient of the driving parameter to be regulated, but (additionally) on the temperature. This may be the environmental temperature of the vehicle, but also the temperature of the pressure medium. In this way it is possible, for instance, to turn on the supplemental source for accelerating the regulation only if either the gradient of the deviation of the parameter to be regulated has achieved a certain value or the temperature lies beneath a certain value. Of course, a mixed parameter can be formed here which depends on both values, so that the lower the environmental temperature, the smaller the gradients for turning on the supplemental source. The application of the process according to the invention is practical in particular for a braking system wherein the gradient of the deviation of the actual value of the regulated parameter from that of the set value.
The invention has proven itself very well for a supplemental pressure medium source when the deviation from the yaw angle, transverse acceleration, steering angle, or velocity is monitored because the switching noises of the source are avoided, and the driving comfort during the case when the vehicle must be regulated is increased.